Method of preparing closures containing a foamed annular sealing liner and thin central portion

ABSTRACT

A PROCESS FOR THE PRODUCTION OF &#34;BOTTLE CAPS&#34; OR CROWN CLOSURES WITH A LINER HAVING A VERY THIN TRANSPARENT CENTRAL PORTION AND A FOAMED ANNULAR RING. THE FOAMABLE VINYL PLASTISOL IS DEPOSITED IN THE INTERIOR OF THE INVERTED CLOSURE. THE DEPOSITED MASS IS THEN SHAPED BY A PLUNGER HAVING A RAISED PORTION IN ITS CENTRAL PORTION. THE SHAPED MASS IS THEN HEATED TO GEL THE PLASTISOL. THEREAFTER, THE SHAPED PLASTISOL IS HEATED TO A HIGHER TEMPERATURE TO FUSE AND FOAM THE PLASTISOL.

Feb. 16, 1971 "i R. PECK METHOD OF EREPARING CLOSURES CONTAINING AFOAMED 3,564,602 ANNULAR SEALING LINER AND THIN CENTRAL PORTIO FiledAug. 29, 1963 I llllllll 1d 7 W (ff United States Patent 0 METHOD OFPREPARING CLOSURES CONTAIN- ING A FOAMED ANNULAR SEALING LINER AND THINCENTRAL PORTION Robert Peck, Elmhurst, Ill., assignor to W. H.Hutchinson & Son, Inc., Chicago, Ill., a corporation of Delaware FiledAug. 29, 1963, Ser. No. 305,361 Int. Cl. 132% 9/06, 9/08, 27/04 US. Cl.264-45 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to themanufacture of closures for containers, and more particularly the lineremployed in such closures to engage in sealing relation with the lip ofa container.

In container closures, and particularly in the closures known as crownclosures or bottle caps, a liner is interposed between the closure andthe lip of the container to be sealed, and is adapted to bear on the lipto seal the container. The liner may take the form of an annular ringadapted to bear on the lip of the container, or the form of a thin diskwith an annular ring projecting from the periphery of one surface of thedisk. The latter form lends itself more easily to automated manufactureand assembly, and such liners are commonly made by putting a quantity ofmoldable material into the cup of an inverted crown cap, and thenpressing down with a punch or plunger to squeeze the material outwardlywith respect to the plunger to form the projecting annular rim, thecentral portion of the disk being formed by the material which remainsdirectly under the plunger.

It has been known in the prior art to form the disk type liners fromsynthetic resin materials, but a relatively great quantity of suchmaterial has been necessary to form a liner which is capable of making agood seal with the container.

The liner must have resilience in order to insure closure of thecontainer, despite any surface irregularities which might exist at thelip of the container. But since the resilient qualities of thecompositions used in the prior art are relatively poor, the annular ringmust have a relatively great thickness to provide enough resilience toform a good seal with the container. This, of course, is an importantfactor in the cost of such closures.

It is therefore an important object of the present invention tomanufacture a closure liner and which method of making the same effectsa saving of material and therefore a reduction in the cost of suchclosures.

Another object of the present invention is to provide a closure having aliner with improved resiliency, without increasing the thickness of theliner.

A further object of the present invention is to provide an improvedmethod of utilizing a composition from which closure liners may beformed.

These and other objects and advantages of my invention will becomemanifest upon an examination of this specification and the accompanyingdrawings and claims.

In one embodiment of the present invention there is provided a method ofmaking an improved closure liner comprising combining a moldablematerial with an expandable material, inserting a quantity of thecombined material into a closure, shaping the material within theclosure to form a liner conforming to the contour of a container lipwith which the closure is to be used, and causing said expendablematerial to expand and increase the thickness and resiliency of theliner.

Reference will now be made to the accompanying drawings, in which:

FIG. 1 is a diametric cross-sectional view of a closure commonly knownas a crown cap, and illustrates the improved liner of the presentinvention; and

FIGS. 2 to 6 are schematic illustrations of separate steps in theprocess of manufacture of the closure liner of the present invention.

Referring now to FIG. 1, the improved liner of the present inventioncomprises a disk having a relatively thin central portion 7 and athicker peripheral portion in the form of an annular ring 8, the linearcovering the substantially p ane surface 9 of a closure 10, the annularring 8 also engaging the side wall 11 of the closure. The shape of theliner is known in the prior art, but the liner of the present inventionhas improved mechanical characteristics, and is formed by a method whichreduces the cost of the liner as compared to prior art liners.

The process by which the liner of the present invention is formed isillustrated in FIGS. 2 through 6, and begins with the alignment of anordinary crown cap 10 with its side wall 11 opening upward asillustrated in FIG. 2. Preferably a number of such caps are fed inseriatim along a conveyor (not shown) or other apparatus for presentingsuccessive caps to successive processing stations at which steps of theprocess to be described are T performed. Such conveying means are wellknown to those skilled in the art and will therefore not be described indetail. The filling position is illustrated in FIG. 3 in which adispenser 12 is operative to dispense a quantity of liner material 14into the central portion of the closure 10. At the next step (FIG. 4),the closure is supported by a support ring 15, and a heated tubularpress or plunger 16 is lowered toward the open end of the closure 10,and a die 18 supported by the plunger 16 is brought into engagement withthe liner material 14, as shown in FIG. 5. The liner material is thensqueezed outwardly with respect to the plunger 16 to form the annularring 8, and to minimize the thickness of the central portion 7.Thereafter, the closure 10 with the formed liner material in place, isbaked in an oven 34 (FIG. 6) to bring about decomposition of a blowingagent included in the liner material 14, and to cure the mainconstituents of the linear material 14. The decomposition of the blowingagent releases gas which is trapped by the liner material in amultiplicity of small pockets, bringing about an expansion of the liner.

The plunger 16 is provided with a forming tip or die 18 which has acontour on its lower surface 20 corresponding to the desiredconfiguration of upper surface of the finished liner. The die 18 isthreadably secured to the plunger 16 by threads 22, to permitinterchange of dies, and to permit adjustment of the position of the diewhen in its lower condition.

The quantity of liner material 14 is a precisely metered amount for eachclosure 10, and the correct amount can easily be determined by trial anderror and adjustment of quantity dispensed by the dispenser 12. When thecorrect quantity is reached, this may readily be recognized by examiningthe cap and its liner material after the depression of the plunger 16.When too much liner material is dispensed into the closure 10, thecentral portion 7 of the liner is unduly thick, while when too littleliner material 14 is dispensed, the annular ring portion 8 of thefinished liner is not fully and completely molded.

The tubular plunger 16 is heated by a heater element 27 disposed withinthe plunger 16, and the support ring is also heated by means of a gasburner or the like 30. By this means, the outer surface of the linermaterial 14 is cured so that the liner holds its shape after removal ofthe die 18.

As has been noted above, it is desirable to minimize the amount of linermaterial necessary to form a satisfactory seal. It is evident that theliner material present at the central portion of the liner is notnecessary to the successful use of the completed closure, since thecontainer is open at this portion, and therefore the central portion ofthe liner performs no sealing function. Accordingly, it is desirable tosqueeze this portion of the liner material 14 as thin as possible, andforce substantially all of the liner material into the periphery of theinterior of the closure where it forms the annular ring 8, while leavinga thin film in the central portion.

'In order to attain consistent results with respect to the physicaldimensions of the liner after it is formed, the plunger 16 is preferablyforced downwardly with precisely the same force during each operation.This is readily accomplished by the provision of a spring 32 disposedexteriorly of the tubular plunger 16, and bearing on a step 33 of thedie 18. The downward movement of the plunger 16 is due entirely to theforce of the spring 32 acting between the plunger 16 and some fixedreference point (not shown) on the frame of the machine holding theplunger 16.

In some cases, it may be desirable, however, to provide a greaterthickness of material 14 in the central section of the liner, forreasons of appearance or the like, and this may be accomplished byvarying the force applied to the plunger 16 by varying the compressionon the spring 32, or by adjusting the position of the die 18 withrespect to the plunger 16 by rotating one relative to the other, toprovide a slightly greater distance between the bottom surface of theplunger and the upper surface of the interior of the liner 7. Especiallyin this case it is desirable for the bottom surface of the plunger 16 torefrain from picking up any of the liner material 14 after the same hasbeen pressed into position, and this is accomplished by forming the dieof a hard material which may be polished to a mirror finish.

In accordance with the present invention, the liner material 14 hasincorporated therewith a blowing agent, by which the size and resiliencyof the liner may be increased during the heating and curing stepillustrated in FIG. 6. It is therefore evident that much less linermaterial, with the blowing agent, is needed to produce the samethickness of the finished liner as compared to liner material withoutthe blowing agent. This brings about a considerable saving in cost ofthe liner. The blowing agent is decomposed by the heat applied by theoven 34 via an infra-red burner or the like 36, and undergoes a chemicalreaction which substantially increases the volume of the blowing agentby releasing a considerable amount of gas, in relation to its volumebefore heating, thereby filling the liner material 14 with voids or gaspockets, and the completed liner thereupon takes on a spongy character,which is partly due to the compressibility of the gas. Accordingly, theresiliency of the liner 14, in addition to its volume, is increased byuse of the blowing agent.

In accordance with the present invention, the liner material 14 is acomposition formed as the fused product of a mixture of solvate ofsynthetic resin material with a plasticizer, a stabilizer, and a blowingagent. Examples of such compositions will now be given, in each of whichexamples the preferred range of amounts of each constituent is given,and also the prefererd amount within each range.

4 EXAMPLE I Parts Vinyl chloride resin powder Plasticizer (di-2-ethylhexyl phth alate) 60 (40-80) Stabilizers (epoxidized oil) 5 (3-10)(Calcium stearate; zinc stearate) 3 61-8) Blowing agent(azodicarbonamide) 0.2 (0.2-2.0)

The above composition, after curing in the oven 34 illustrated in FIG.6, forms a liner which is substantially transparent at the centerportion thereof, due partly to the relatively good light transmissioncharacteristics of the composition, and the relatively thin nature ofthe center section of the liner. In a crown cap, the center portion 7 ofthe liner is approximately /1" in diameter and has an average thicknessof between 0.002" and 0.008". Therefore, the composition of Example Ican advantageously be employed to produce a transparent window or thelike through which pictures or advertising material, etc., are visibleon the interior surface of the closure 10.

EXAMPLE 'II Parts Vinyl chloride resin power 100 Plasticizer (di-Z-ethylhexyl phthalate) 60 (40-80) Stabilizers (epoxide oil) 5 (3-10)Stabilizers (calcium stearate, zinc stearate) 3 (1-8) Blowing agent(azodicarbonamide) 0.2 (0.2-2.0) Titanium dioxide 2.4 (l-10) Carbonblack 0.05 (0.05-5.0)

The composition of Example II is similar to that of Example I, with theexception of the provision of a pigment comprising a mixture of titaniumdioxide and carbon black. This gives the composition a gray appearance,which may be lightened or darkened by varying the proportion of the twopigment materials. This composition is substantially opaque, even in therelatively thin central portion 7 of the liner 14, and therefore may beused to hide imperfections in the interior surface of the closure 10, ifany, and to provide a uniform appearance of the interior of the closure.

In both of the above examples the plasticizer forms a solvate with theresin which makes it sufiiciently moldable to be ejected by thedispenser 12. The stabilizer is included for the purpose of preventingunwanted heat generated reactions in the solvate, and the blowing agentis provided for the purpose which has been already indicated. When theblowing agent is heated during curing of the finished cap, it increasesthe thickness of the annular rim by 25% to 60%, with a correspondingdecrease in density. The exact amount of increase in thickness dependsupon the concentration of the blowing agent within the composition, andthe length of the heating and curing step in the oven 34. Instead ofazodicarbonamide, the blowing agent may alternatively beN,N-dimethyl-dinitrosoterephthalamide which also operates satisfactorilyas a blowing agent.

The composition of the liner material may also include, if desired, wax,wetting agents, fillers, additional pigments, or internal dye releaseagents, each of which may readily be added by those skilled in the artto produce specific desired effects which are well understood.

In formulating the composition, the wax, wetting agents, fillers,pigments, etc., are dispersed into part of the plasticizer such as bymelting or milling, or both. The choice of melting or milling dependssomewhat upon the melting point of the fillers, etc., which are to beadded. The total weight of the resin is blended with a sufiicient amountof the plasticizer to produce a high viscosity dispersion, and then thepigment and filler dispersion is combined with the resin dispersion andthe mixing continued until the batch is uniform. Then the remainingplasticizer, stabilizer and the blowing agent are added, and mixing iscontinued until all of the ingredients are uniformly dispersed. Duringall of the above mixing steps, the temperature is maintained below atemperature of 110 F. to prevent fusion of the resin and theplasticizer, and on the completion of the mixing, the batch is deaeratedin the usual manner to remove en trained air from the mixture.

The dispenser 12., as has been pointed out above, dispenses apredetermined amount of the liner composition during the step in theprocess illustrated in FIG. 3. With respect to crown caps of the typeillustrated, the preferred amount of composition to be deposited isbetween 200 and 400 milligrams. During the forming step illustrated inFIGS. 4 and 5, the temperature of the plunger 16 and the support ring 15are held at between 260 F. and 340 F., by the heating element 27 and theburner 30, and about forty pounds of pressure is applied to the plunger16 by the spring .32 for three to six seconds. The preferred temperatureis about 300 F. and ordinarily four seconds is sufficient to completethe molding step. In the oven 34 illustrated in FIG. 6, the closures areexposed for about /2 minute to one minute to a term perature between 375F. to 450 F. with an exposure of about one minute and a temperaturerange of 400 F. to 425 F. being preferred to fuse the plastisol anddecompose the blowing agent to bring about the above described increasein thickness and resiliency of the liner. As those skilled in the artwill appreciate, the times and temperatures required within the fiuxingoven 34 are interdependent, a higher temperature performing the desiredstep with less time and vice versa. After the completion of the curingin the oven 34, the closure 10 is carried away by means of a conveyorbelt 3 8, which is preferably long enough to permit the closures to coolsufiiciently to be readily handled when they reach the end of theconveyor 38.

Although the present invention has been specifically described for usewith crown caps, the present invention may be used to form liners on avariety of closures, and achieves the same advantages when used in theproduction of other types of closures as on crown caps.

The foregoing will so fully and completely describe the presentinvention as to permit others skilled in the art, by applying currentknowledge, to adapt the same for use under varying conditions of servicewithout departing from the essential items of novelty involved, whichare intended to be defined and secured by the appending claims.

What is claimed is: 1. A method of preparing closures containing aprotective and sealing liner material characterized by a transparentcentral portion which method comprises:

depositing a measured quantity of a vinyl resin plastisol containing ablowing amount of a chemical blowing agent in the interior of aninverted closure;

forming and gelling the plastisol within the closure under heat and byapplication of pressure at a temperature insufiicient to substantiallydecompose the chemical blowing agent thereby producing a relatively thinweb central portion having a web thickness of about 2 to 5 mils inthickness and a relatively thick outer ring portion;

heating the formed plastisol in the closure to a temperature sufficientto decompose the chemical blowing agent and to fuse the plastisolthereby providing a transparent fused central web portion and a cellularopaque ring portion of the vinyl plastisol.

2. The method of claim 1 wherein the vinyl plastisol is formed by aheated contoured punch inserted into the closure a controlled distancesufficient to produce a residual web thickness of about 2 to 5 mils.

3. The method of claim 1 wherein the vinyl plastisol is heated to anon-fluid gelled state prior to being formed into the desired shape.

4. The method of claim 1 wherein the plastisol is formed into a roundedshaped thickened O-ring portion.

5. A method of preparing closures including the steps of:

depositing a measured quantity of vinyl halide plastisol containing ablowing amount of a chemical blowing agent into the interior of aclosure; forming and gelling the plastisol within the closure byinserting a molding punch into the interior of the closure and applyingsufficient heat thereto through the punch for a sufficient time toproduce a nonfluid, shaped gel, said heat being insufficient to causesubstantial decomposition of the chemical blowing agent and said punchforming said shaped gel into a relatively thin circular central webportion having a thickness of about 2 to about 5 mils and a relativelythick outer ring portion; retracting the heated punch; and heating theshaped, gelled plastisol in the closure to a temperature of about 375 to425 F. for a time sufiicient to decompose the chemical blowing agent andto form an expanded, opaque, cellular, fused ring portion and a thintransparent circular fused web portion. 6. The method of claim 5 whichincludes additionally 35 providing a metal closure having an interiorcontaining a predetermined visually observable design in the centerthereof, the plastisol being of a kind which is substantiallytransparent in the non-cellular fused state, whereby upon formation ofthe thin web portion, the design 40 will be observable.

7. A method of preparing closures containing a protective and sealingliner material which comprises:

depositing a measured quantity of a vinyl resin plastisol containing ablowing amount of a chemical blowing agent in the interior of aninverted closure;

forming and gelling the plastisol within the closure under heat and byapplication of pressure at a temperature insufficient to substantiallydecompose the chemical blowing agent thereby producing a relatively thinweb central portion and a relatively thick outer ring portion;

heating the formed plastisol in the closure to a temperature sufficientto decompose the chemical blowing agent and to fuse the plastisolthereby providing a fused central web portion and a cellular ringportion of the vinyl plastisol.

References Cited UNITED STATES PATENTS 6/1967 Strickman 215-40 9/1967Strickman 215-40X

